If you are comparing structural timbers, you might wonder the difference between natural solid timbers and Engineered beams such as Glulams or LVLs. Every kind of wood has different strengths, advantages, and disadvantages. You can choose premium-grade material, but used or installed improperly can cause failure in your structure.
In Manufactured/Engineered beams you have several options falling under the APA approved building requirements. The two most common we deal with are the Glulams and LVLs.
Glulams (aka LamStock) are a versatile product made from several layers of dimensional lumber. They are bonded together with moisture-resistant adhesives to create a sizeable structural member, that can be cut or built into different shapes. These are often used for ceiling and roof beams, columns, stiffeners, and decks. They are a structural wood product that can span long distances without additional support due to the cross grain. Glulams appearance are semi-modern, and resistant to fire and moisture from the laminating process. Although glulams are more expensive than other types of lumber, it is considerably less costly than steel. This structurally superior option is typically more expensive than SCLs also, but has several advantages.
Glulam is lighter and easier to work with than concrete beams and has excellent structural properties. It is one-third the weight of concrete, yet it can be as strong as concrete. Another advantage of glulam is that it offers a natural appearance and does not deform or warp like steel. It can also be improved through fine-proofing finishes, making it a better choice for construction projects that require strength and beauty.
Glulam beams are usually custom built for a specific job, and often arrive on site already finished, meaning that they are sanded, stained, or may have some other final finishing product already added to them. Again, Glulam beams are much lighter than steel, and concrete, but are so strong that you can have them span longer distances than natural timbers. Even old growth trees are NOT as strong as glulam beams with their adhesives and sandwiching of grain patterns. Oftentimes deforestation is slowed because second growth forests, and smaller trees, along with the branches, are harvested in appropriate cycles, because for the engendered timbers it is just the fibers that they are after.
You will see glulams used in the construction of massive commercial builds, but you will probably never see an LVL in the open. They are buried in the walls, specifically over door and windows. Sometimes they are used for decks, or when a home has a second floor that is cantilevered out, but even then, they will need to be covered up eventually with exterior finishing products.
LVLs (Laminated Veneer Lumber, Micro Lam) Fall under the term Structural Composite Lumber (SCL) which was coined to capture a wide array of products, some of which are proprietary or unique to only one manufacturer. SCLs include; LVLs, parallel strand lumber (PSL), laminated strand lumber (LSL) and oriented strand lumber (OSL) per the ADA website.
LVLs, like to GluLams, are layers of wood glued together. However, LVLs are made from cross-laminated wood veneer and does not offer all the same benefits as Glulams. LVLs are made by first making sheets that have wood fibers all running in the same direction (a Veneer), and building out the member (firring) but adding multiple sheets onto one another in 90° grain orientations, until you reach the desired thickness, similar to plywood. Resin is added, and the sheets are squeezed together to produce the final board. The resin that binds the wood fibers is extremely strong, and this contributes to the strength of the beam. You can manufacture them to any engineer’s specifications. Sometimes LVLs are used as vertical members for “tall walls”, which are design features in custom homes, and commercial buildings. Usually, they are used around staircases or elevator shafts where they would not be seen. The edges of the beam show this variation of end grain and long grain. Because of this, they are usually intended to be used as framing that will be covered by a finished wall.
LVLs are usually 1–3/4″ thick, whereas a normal 2x10 is only 1–1/2″ thick. LVLs are more dense than regular wood and therefore provide structural strength over longer spans. For example, if you have a feature wall with 12′ of windows, or a garage door that was 16′ wide, you would most likely use LVLs for the headers. (The wood placed above the opening). Its purpose is to bare all the weight from above the opening and distributed it evenly across the beam to the support studs down to the foundation. Sizes required will depend on the load and local building codes.
All Engineered lumber falls under the APA regulations. Glulams and LVLs are no exception. For more detailed information regarding the versatility and many options on these types of materials visit the APA site at www.apawood.org